Instructions: This is a 2.7 file, open on 2.79, and then on 2.8 git.8839152abf5
Turn on and off the subdivisions modifier of each cilinder, one by one, and compare the performance on both versions of blender, pressing play

I set up the scene to be 60fps so that's the baseline. In both 2.79 and 2.8, without subdivisions, the animation plays at 60fps

Subdividing the cilinder with just quads, at 4 levels and 1 quality, gives me 55ish fps in 2.79, and around 40fps in 2.8
Meanwhile, subdividing either the cilinder with Ngons or the one with triangles fan, goes from 60fps on 2.79, to around 20fps in 2.8. This is what I was refering to about slow Ngons, or vertices fanning lots of triangle faces